This invention relates to fluid flow regulating systems and to motor speed control systems and devices for use with fluid pumping equipment such as forced air cooling fans and blowers.
Cooling fans are used for cooling work areas and electronic equipment housing areas to name but a few of such uses. In most industrial work area cooling applications, the fan speed is unregulated and the area temperatures accordingly fluctuate in dependency, among other things, upon the ambient air temperatures being delivered to the work area. At times, the airflow determined by the operating speed of the fan motor produces excessive cooling and uncomfortable conditions for the workers in the area. Apart from this, fans are a recognized source of noise pollution, and it is known that the noise level produced by a fan is roughly proportional to the fan speed. The unregulated flow of air in excess of the area demands is additionally wasteful of energy.
For electronic equipment cooling purposes, the general practice followed in selecting forced air fans for cooling the equipment has been one of selecting the fan which, at its continuously energized operating speed, will remove the greatest amount of heat that will be generated by the equipment during an operating cycle and under the highest ambient temperature and lowest pressure conditions that will be encountered in use of the equipment. This practice, in the absence of systems for regulating the fluid flow in accord with the demands of the equipment, leads to excessive operating costs and unnecessary noise pollution. Apart from this, the deposition of dust on electronic equipment is a factor of importance, since dust layers retard heat transfer and are deposited at a rate directly proportional to the airflow into contact with the equipment. As such, an unnecessarily short interval between cleaning cycles is encountered in most installations that fail to provide for adaquate fluid flow regulation in accord with the cooling demands of the equipment.
To overcome some of these problems, some systems have been developed and where the motor circuit is interrupted when the air temperature diminishes to a predetermined value. In such systems, the fan ceases to operate and there is a time lag before the fan motor is again energized and responds to a detected area temperature change. During the interim, no area cooling is accomplished. This type of interrupted operation is suitable for some work area cooling applications. However, in electronic equipment cooling applications, an interrupted flow of air is unsatisfactory because the rate of temperature rise for some electronic equipment components is greater than for others, and the sensors used must, for practical purposes, sense area rather than specific component temperatures. Other control systems for fan motors provide for a continuous flow of the cooling media but rely upon varying the resistance in the motor circuit to regulate the motor speed, a practice which fails to diminish the operating costs in accord with the diminished cooling demand. Such systems are also expensive to manufacture and install and are frequently unreliable in their operation.